These types of electronic component comprising at least one chip (or integrated circuit) operating at millimetric frequencies have applications in particular in the automobile radar field. In these types of application, an electromagnetic wave is transmitted at a millimetric frequency and the wave reflected by an obstacle is received by an antenna, in order to extract from this wave distance information, on the one hand, and relative speed on the other hand, between this obstacle and the source that transmitted the wave. For this purpose, the vehicle is equipped with a system comprising radars positioned all around the vehicle for detecting objects. Long-range radars, for example operating at 77 GHz, are positioned at the front of the vehicle and short-range radars, operating at 24 GHz and 79 GHz, are positioned on the rear and along the sides of the vehicle.
The distance and relative speed information is transmitted to a central processing unit of the system which ensures, for example, that the vehicle is kept at a specified distance from the objects or from another moving vehicle traveling on the same road.
The objective of these systems using automobile radars is firstly to provide driving comfort with functions for servocontrolling the speed of the vehicle relative to another vehicle preceding it, but also to signal potential hazards.
In general, these systems using automobile radars comprise elementary frequency generation and microwave transmit/receive functions.
The components operating at millimetric frequencies may also be used for short-range very high-data-rate communication applications.
Whatever the application, the electronic processing of millimetric-frequency signals includes a low-frequency processing part that may be carried out by silicon integrated circuits mounted on printed circuits. This part may be carried out by very well-established and low-cost technologies, with connections that are simple to produce between circuit elements on one and the same integrated circuit chip or between various integrated circuit chips. The processing also includes a part of very high frequency (above 45 GHz), which can be implemented only by components and integrated circuits made of semiconductor materials suitable for microwave applications (gallium arsenide GaAs, and especially its derivatives, or else SiGe). These integrated circuits are called MMICs (microwave monolithic integrated circuits). This very high-frequency part poses difficult production problems and in general turns out to be very expensive.
For relatively complex functions, components are encapsulated in a metal package containing a large number of MMIC chips, the quantity of circuit elements that can be placed in one and the same chip being more limited in the case of MMIC circuits than in the case of low-frequency silicon circuits. These chips are mounted on a substrate having interconnections that are difficult to produce and therefore expensive, owing to the very high frequencies at which they work.
Mounting chips on a hybrid substrate (mounting in general with wire bonding to connect the chips to the hybrid substrate) is itself very expensive when there are many chips to be mounted.
These components include, especially in the case of automobile applications, contactless access ports operating by electromagnetic coupling for transmitting and receiving the waves.
Transmission by electromagnetic coupling at these very high frequencies is accomplished by using the free propagation properties of electromagnetic signals inside the package and in particular between the inside and the outside. This package includes in particular a conducting cap (a metal or metallized cap) that encloses the signal propagation lines coming from the chip or going to the chip. The conducting cap is located above the external contactless access port, at a distance such that it constitutes (at the main working frequency for which the component is designed) an electromagnetic short-circuit promoting free-propagation signal transmissions via this access port.
Access ports at the working frequency F0 of more than 45 GHz are transitions by electromagnetic coupling in the air (or in a gas or in a vacuum) and especially conducting elements capable of radiating toward a waveguide placed facing these elements, or capable of receiving electromagnetic radiation output by a waveguide in front of which they are placed. The package in which the MMIC chips are contained includes a nonconducting part facing these conducting elements so as to let the electromagnetic energy pass between the waveguide and the conducting elements.
FIG. 1 shows a component of the prior art for automobile applications. The component is encapsulated in a package 10 that includes a contactless electromagnetic access port 12.
The component comprises a metal base 14 serving as substrate on which there are directly mounted, via its rear face 16, an MMIC microwave chip 18, a double-sided ceramic substrate 20, serving for interconnections to the inside of the package and to the outside of the package, and a metal or metallized cap 19 covering the base, in order to enclose, between the base and the cap, the chip and the ceramic substrate 20. The MMIC chip 18 is soldered directly to the base 14.
The ceramic substrate 20 is preferably a substrate metallized on both its faces 24, 26, comprising metallizations 30 on its front face 24, in order to form transmission lines, and metallizations 32 on its rear face 26, in order to form a ground plane.
The dimensions of the various dielectric and conducting parts are such that the component operates correctly at the working frequency in question F0 (77 GHz). The metallizations 30 and 32 serve on the one hand to establish interconnections between chips and, on the other hand, to establish the external access ports of the package.
The access port 12 of the component shown in FIG. 1 comprises a contactless electromagnetic coupling transition allowing the signal at the frequency of 77 GHz to pass, contactlessly, from a waveguide to the MMIC chip 18, or vice versa.
This electromagnetic coupling transition is preferably made by means of an aperture 36 in the package 10, and more precisely in the metal base 14.
The substrate 20 includes a radiating element 38 communicating for example with a waveguide placed in front of the aperture 36, the radiating element acting as element for receiving and transmitting an incoming or outgoing electromagnetic wave in the package.
The electrical connections between the substrate 20 and the chip 18 are produced by wire bonding.
The component includes other access ports 44 operating at frequencies below those of the microwave access port. The MMIC chip is also connected to these other access ports 44 by wire bonding 46.
The component is connected to another, similar component or to a different component mounted on a conventional printed circuit via the other access ports 44.
In the automobile radar application, the increase in number of functionalities of such systems entails the use of an increasingly large number of detection radars all around the vehicle and thereby requires greater effort to reduce the costs of the elementary functions of the system.
One of the major problems for these automobile applications is the cost of the millimetric transceiver module. This cost results from the components used, but also from the assembly technology used to fabricate these modules.
The existing solutions do not allow the market-driven cost objectives to be achieved. These solutions are limited for two essential reasons, namely the implementation cost (equipment, training, reproducibility) and the production costs.